Atomic Models and Subatomic Physics

Flashcards covering the scientists, key experiments, historical models, and subatomic discoveries in atomic theory.

John Dalton

English chemist, physicist, and meteorologist who transformed ancient philosophical ideas into a quantitative scientific model in 1803 by proposing that matter is made of indivisible atoms.

"Billiard Ball" Model

The atomic framework proposed by John Dalton, which presented atoms as solid, indivisible, and indestructible spheres that combine in simple, fixed ratios.

Isotopes

Atoms of the same element that vary in mass due to differing neutron counts, representing a key limitation of Dalton's atomic model.

Sir Joseph John Thomson

Nobel Prize-winning British physicist who discovered the electron in 1897 using cathode ray tubes and created the "Plum Pudding" model.

Electron

A negatively charged subatomic particle discovered in 1897 by J.J. Thomson through experiments with cathode ray tubes.

"Plum Pudding" Model

An atomic model proposed by J.J. Thomson featuring negatively charged electrons embedded within a uniform, positively charged sphere.

Ernest Rutherford

New Zealand-born British physicist and Nobel laureate recognized as the father of nuclear physics, who discovered the atomic nucleus and protons.

Gold Foil Experiment (1909)

An experiment conducted by Ernest Rutherford where positively charged alpha particles were fired at thin gold foil, revealing that atoms consist mostly of empty space.

"Nuclear" Model

Ernest Rutherford's 1911 atomic model establishing that an atom's mass and positive charge are concentrated in a tiny central nucleus, with electrons orbiting in empty space.

Proton

A discrete, positively charged fundamental particle located in the nucleus, named by Ernest Rutherford in 1920.

James Chadwick

The scientist who discovered the neutron in 1932, resolving the missing neutral mass problem of atomic nuclei.

Niels Bohr

Danish physicist awarded the Nobel Prize in Physics in 1922 for applying quantum theory to atomic structure and creating the "Planetary" model.

"Planetary" Model

Niels Bohr's atomic model proposing that electrons orbit the nucleus only in specific, fixed circular paths called energy levels.

Quantized Energy Levels

Specific, fixed circular orbits where electrons reside around the nucleus without continuously radiating energy.

Excited State

The condition of an atom when an electron absorbs a precise photon of energy to jump to a higher energy level.

Ground State

The lower energy level an electron drops back to when emitting a photon equal in energy to the absorbed photon.

Werner Heisenberg

German theoretical physicist and key architect of quantum mechanics who formulated the Uncertainty Principle.

Uncertainty Principle

A principle proved by Werner Heisenberg stating that it is physically impossible to simultaneously measure both the precise position and momentum of a subatomic particle.

"Electron Cloud" Model

The modern quantum mechanical model developed by Werner Heisenberg and Erwin Schrödinger, describing electron positions using mathematical probability distributions.

Orbitals

Three-dimensional probability distributions where an electron's location is treated as a cloud of varying density.